Birds of the world, beware: Living among humans can be dangerous. Fliers often become confused by the near-invisibility of window glass and crash into houses and tall buildings. Some larger birds may be poisoned when they feed on carcasses tainted with lead from shotgun pellets. But the really big killer: Puss.

Cats kill between 1.4 billion and 3.7 billion birds every year in the United States alone, a new report concludes. That’s nearly a billion more birds — at least — than estimated by...